Bicycle Mechanics - 9 Speed Cassette on 8 spd Sora RD Brifters

I'd like to swap out the 8 speed SRAM cassette on my wife's Fuji (Sora RD, Sora Brifters) for a 9 speed cassette. From reading a few posts from searching, it looks like it's not compatible to USE 9 gears without changing the brifters and maybe the RD. However, if I'm not worried about her being able to use all 9 gears, would the setup still work and shift well? Why bother, you ask? Well, my bike has a 9 speed drivetrain and if we have 2 bikes, I'd like to be able set hers so I can easily swap wheels in an emergency. My rim is at the LBS to be rebuilt due to an "unfortunate weird event", so I've substituted hers on mine, but need to adjust the RD to have it shift well. Putting a 9 on hers would streamline this if I need to do it again. I don't want her to lose function or have poor shifting as a result, though.

The alternative is fixing up the old 12 speed Fuji as a backup bike, but that requires new cranks, front rings and possibly a new brake and FD, thanks to damage from a truck.

8 and 9 speed cog spacing is different.

http://www.sheldonbrown.com/cribsheet-spacing.html

In other words, no.

-Z

Move your 9 speed cassette over to your wife's rear wheel when you want to use her wheel on your 9 speed bike. It is a simple job, and the tools you need are cheap (chain whip).

Interesting thought, just moving the cassette. In general, if I was somewhat practiced at it, how long would you expect to need to do it? One of the times I've used it in the past is when grabbing my bike to ride & finding my tire to be flat. In the current case of my wheel being in the shop for rebuilding, I'd have more time to make the switch, but other times it would be last-minute.

Interesting thought, just moving the cassette. In general, if I was somewhat practiced at it, how long would you expect to need to do it?

I'd project 5 minutes for everything - remove both rear wheels, swap cassettes, and replace the rear wheel onto the bike that you're riding.

Wow thanks. I've never removed a caseete and had no idea it be that quick.

Wow thanks. I've never removed a caseete and had no idea it be that quick.
And that 5 mins includes stopping for a beer mid-way through! Piece of cake. Go for it, mate.